Method for checking validity of bulgarian EGN codes.

egn_checker.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
#       egn_checker.py
#       
#       Copyright 2011 Venelin Stoykov <[email protected]>
#       
#       This program is free software; you can redistribute it and/or modify
#       it under the terms of the GNU General Public License as published by
#       the Free Software Foundation; either version 2 of the License, or
#       (at your option) any later version.
#       
#       This program is distributed in the hope that it will be useful,
#       but WITHOUT ANY WARRANTY; without even the implied warranty of
#       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#       GNU General Public License for more details.
#       
#       You should have received a copy of the GNU General Public License
#       along with this program; if not, write to the Free Software
#       Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
#       MA 02110-1301, USA.

def egn_checker(egn):
    '''
    Check Bulgarian EGN codes for validity
    full information about algoritm is available here
    http://www.grao.bg/esgraon.html#section2
    '''
    def check_validation_code(egn):
        _weights = (2, 4, 8, 5, 10, 9, 7, 3, 6)
        try:
            my_sum = sum([weight * int(digit) for weight, digit in zip(_weights, egn)])
            return int(egn[-1]) == my_sum % 11 % 10
        except ValueError:
            return False

    def check_valid_date(egn):
        from datetime import datetime
        try:
            year, month, day = int(egn[0:2]), int(egn[2:4]), int(egn[4:6])
        except:
            return False
        if month >= 40:
            month -= 40
            year += 2000
        elif month >= 20:
            month -= 20
            year += 1800
        else:
            year += 1900
        try:
            datetime.strptime('%s-%s-%s' % (year, month, day), "%Y-%m-%d")
            return True
        except ValueError:
            return False

    return len(egn) == 10 and check_validation_code(egn) and check_valid_date(egn)

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